This disclosure relates to relaying of communications by a mobile device in a communication system.
A communication system can be seen as a facility that enables communication sessions between two or more entities such as mobile communication devices and/or other stations associated with the communication system. A communication system and a compatible communication device typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the manner how the communication device can access the communication system and how communications shall be implemented between communicating devices, the elements of the communication network and/or other communication devices is typically defined.
In a wireless communication system at least a part of communications between at least two stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (KEN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). In wireless systems an access node is provided by a base station. The radio coverage area of a base station is known as a cell, and therefore the wireless systems are often referred to as cellular systems. In some systems a base station access node is called Node B.
A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. A communication device may be arranged to communicate, for example, data for carrying communications such as voice, electronic mail (email), text message, multimedia, for enabling internet access and so on. Users may thus be offered and provided numerous services via their communication devices. The communication connection can be provided by means of one or more data bearers.
In wireless systems a communication device provides a transceiver station that can communicate with the access node and/or another communications device. A communication device or user equipment may also be considered as being a part of a communication system. In certain applications, for example in ad-hoc networks, the communication system can be based on use of a plurality of user equipment capable of communicating with each other.
A feature of wireless communication devices is that they offer mobility for the users thereof. A mobile communication device, or mobile device for short, may also be transferred, or handed over, from a base station to another and even between base stations belonging to different systems.
3rd Generation Partnership Project (3GPP) is standardizing an architecture that is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The aim is to achieve, inter alia, reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. A further development of the LTE is referred to herein as LTE-Advanced. The LTE-Advanced aims to provide further enhanced services by means of even higher data rates and lower latency with reduced cost. The various development stages of the 3GPP LTE specifications are referred to as releases.
Since the new spectrum bands for international mobile telecommunications (IMT) contain higher frequency bands and LTE-Advanced is aiming at a higher data rate, coverage of one base station may be limited due to the high propagation loss and limited energy per bit. Relaying has been proposed as a possibility to enlarge the coverage. Apart from this goal of coverage extension, introducing relay concepts may also help in the provision of high-bit-rate coverage in a high shadowing environment, reducing average radio-transmission power at the user equipment. This may provide improved battery life, enhanced cell capacity and effective throughput. Relaying may also reduce deployment costs of radio access networks (RAN).
In the LTE-A architecture a relay node may communicate with a base station such as a donor eNodeB (DeNB). The DeNB may act as a proxy for the relay node when the relay node communicates with other entities as discussed in 3GPP TSG RAN WG3 #68 and 3GPP TSG-RAN WG3 #66bis. In this way the DeNB allows correct establishment of interfaces, such as the X2 interface, and ensures non-user equipment signalling is conveyed to and from the relay node appropriately.
A relay node associated with a particular DeNB is considered part of the cell of the DeNB with respect to other entities such as base stations in the system. In practice a relay node associated with a DeNB may share the same eNB identification with the DeNB in order to allow neighbouring relay nodes to identify the relay node and communicate with the DeNB associated with the relay node.
Some interfaces, such as the X2 interfaces were designed as a point to point interface. For example an X2 interface may have been previously used to communicate between two base stations. However with the introduction of relay nodes associated with a base station, for example as used with the LTE-A architecture, the X2 interface may not operate as a point to point interface as originally designed. This can lead to an uncertainty for the type of handover for a user equipment a relay node may initiate. This may also mean that messages cannot be delivered to the correct relay node associated with a particular base station.